This invention relates to electrical devices and, more particularly, to multiple phase inductors.
Power inverters, converters and the like include inductors which must carry high currents in their coils. The size and weight of these inductors is dependent upon the ability to dissipate heat produced by this current flow. High current inductors have been constructed to include a single layer wound coil with the coil being exposed to some coiling media such as air or oil. To improve cooling, individual turns of the coil have been spaced apart so that coolant will reach the sides of each turn in addition to the outer edges of the turns. Even with single layer coils having spaced apart turns, these devices may represent a large percentage of the inverter or converter total weight.
A typical three phase inductor for use in an aircraft power source may include two laminated "E" shaped cores of silicon steel with three single layer coils of a rectangular conductor wound on edge around the legs of the cores. The core dimensions, number of coil turns, and the coil conductor size are all dependent upon the desired power rating. To achieve the desired inductance, there are typically three gaps in the core which are placed at the center of each leg. The size of the gap is also dependent upon rating but typically varies from 0.25 inch to 0.50 inch.
The turns of the coil which are wound over or in close proximity to the gap space in the core may be subjected to substantially higher temperatures than the other turns of the coil. In high power rated air cooled inductors, the local heating of particular coil turns can cause failure of those turns. This local heating is caused by flux fringing around the gap space in the core. The flux penetrates the coil turns and causes high eddy currents. Since the coil conductor is rectangular and presents its largest surface area to the flux path, the heating normally is worse than it would be with round or flat conductors. However, rectangular conductors are used to conserve weight and to reduce the size of the inductor.
A secondary problem faced by such inductors is an imbalance in the inductance between the center leg and the outer legs. This imbalance is typically corrected by reducing the core size (number of laminations) for the center leg.
This invention seeks to provide a segmented core inductor which is resistent to failure caused by localized heating of selected turns of the inductor coil, while at the same time providing equal inductances for each coil.